A wide variety of lettuce-type greens including tango, lolla rosa, red oak leaf, baby romaine, green oak leaf, baby red romaine, baby leaf spinach, baby red chard, red mustard, Totsoi, Mizuma, Frisee, arruagula, radicchio, and curly endives are currently grown, and are known in the trade under the term "baby greens". They are used for mixed or one of a kind salads and garnishes. They are ordinarily grown in raised beds which range in width from 36 to 48 inches between furrows. They are harvested well before maturity for freshness and tenderness. Current harvesting technique is entirely manual, and involves the farm laborer kneeling, leaning across the bed and severing the stems adjacent the earth with a knife or sickle. The laborer then places the severed greens by hand into carrying boxes called "totes" which are stacked in pallets, typically 24 totes per pallet. This work is, to say the least, hard on the knees and back, grimy, sweaty and unappealing. Typical harvesting rates are approximately 4 person-hours to produce 20 totes. The preferred cutting time is usually from 6:00 or 7:00 to 10:00 in the morning, after which it may become too hot as the cut greens wilt too fast to be a useful product. Thus, in a 3-hour "cutting day" or "cutting period" one worker produces only 15 totes, or about less than 75% of a pallet.
Shelf life is critical to greens marketing. It takes considerable time from harvest for the greens to pass through processing and distribution to market, and wilted and bruised greens are unsalable. In turn, gentle handling is a key to long shelf life. While great care is taken to process, transport and display lettuce and other greens under refrigerated conditions, these steps do not address the initial problem of bruising, tearing, scraping and pinching during harvesting. To minimize damage, greens must be severed without pulling, tearing or shredding, and must be handled gently in the field. Greens crush and bruise easily, and subsequently wilt and discolor to brown within a matter of hours. For example, on a cool day the wilting/discoloration is well along within three hours, and on an 80.degree. F. day, within two hours. If the greens are damaged during harvesting, downstream gentle handling does not reverse the initial damage. The longer a delay in getting greens from the field into processing, the worse the problem.
There are a wide variety of self-propelled harvesters and pickers, but there are none specially designed to handle the extremely fragile and wilt-prone baby greens, which are a specialty produce. For example, the "Dalgety" harvester, shown in U.S. Pat. No. 4,967,545 of Fischer et al. (1990), is a towed machine for harvesting full grown spinach. It employs a sickle bar mounted on a wheeled frame and a single continuous air permeable belt (typically 15% open area ) from a point behind and above the sickle bar to a higher rearwardly located point. The belt is covered by a housing. A fan is disposed below the belt and operates as a vacuum plenum to suck cut greens onto the belt where they adhere while they are being transported upwardly and rearwardly by the belt to be discharged Into receiving containers or a side discharge conveyor. This machine has not proven especially popular, at least in part due to the fan requirement, the suction from which results in fragile greens being bruised by being drawn into or partly through the belt foramina. Also, once a greens leaf covers belt openings, the suction is substantially reduced or lost altogether, and the carrying capacity of the belt is correspondingly reduced or nullified. The downward fan discharge also can produce large qualities of dust that contaminates cut produce, and adjacent rows of uncut greens.
With the increased emphasis on healthy choice in food, it would be beneficial to have an automated self-propelled greens harvester which could be more productive and result in a more efficient harvesting of a fresher, less bruised product, while at the same time relieving workers of the back-breaking nature of hand labor.